Boiler construction



March 15, 1949. H. w, LYKE 2,464,701

BOILER CONSTRUCTION Filed Sept. 10, 1945 Y 2 Sheets-Sheet 1 March 15, 1949. H. w. LYKE BOILER CONSTRUCTION 2 Sheets-Sheet 2' Filed Sept. 10, 1945 Jawcmto'b Patented Mar. 15, 1949 UNITED STATESlPATENT OFFICE Application September' 10, 1945, Serial No. 615,307

'1 cities" (01. 122-149) This invention relates tocertaln improvements in boiler construction for steam'generatorsand" the like; and the nature and objects of? theinvention will be readily recognized and understood by those skilled in the arts to which the invention pertains, in the light of the followingde= scription and detailed explanation of the -accompanying drawings illustrating what I now con-'1 sider to be a preferred embodiment and mechanical and structural expression of my invention,

from among various other embodiments, expres in its utility, to boilers of'the horizontal and/or l of the fluid fuel burning types; P

It is a general object of my present invention to improve the design and construction "'and' thereby increase the efiiciency of operation, of steam boilers of those types having a gas recir-f culating chamber at one end thereof for receiving combustion gases from a combustion tube for recirculation from said chamber through the boiler.

A further and more specific object is to e1im'i-'"' nate or substantially reduce the possibility of" structural failures such as fractures, cracl;s or the like in the wall structure of such a 'gas recirculating chamber which may be caused by the extremes of temperature .to which the wall" structure is subjected. h 7

And another object isto provide a design and construction of boiler having such a gas recirculating chamber by which "a gas receivingchamber is formed in the boiler around and surrounding the outer portion of the gas recirculating chamber with a minimum of area of 'the' side wall structure of the gas recirculating cham the design and construction thereof, all as will be fully referred to hereinafter.

Referring to the accompanying drawings in which similar reference characters refer to corresponding parts and elements throughout the several figures thereof.

Fig. 1 is a view in vertical, longitudinal section through a form of horizontal fire tube type of boiler for a steam generator, embodying a design and construction of gas recirculating chamber forming head structure at one end of the boiler designed and constructed in accordance with my present invention.

Fig. 2 is a view in end elevation of the boiler of Fig. 1 with the removable outer end wall of the recirculating chamber "forming head structure, removed from the boiler, and particularly showing the unitary end wall and recirculating cham ber peripheral side wall of the recirculating" chamber forming head structure of my invention.

Fig. 3 is a view in vertical longitudinal section through the recirculating chamber forming head structure of the boiler of Fig. 1, taken as on the line 3-3 of Fig. 2, but with a portion only of the boiler being shown.

I have selected, andhave illustrated and described herein, by way of example, a boiler embodying my invention, of the horizontal fire tube type having a horizontally disposed generally v centrally located combustion tube therethrough designed for use with'fluid fuel, such as oil or gas, such type of boiler being particularly adapted V for use with steam generator units. However, it"is to be understood that my invention is not limited to adaptation anduse with this particular type and design of boiler, but is adapted for use her being exposed to the surrounding gas receiving chamber. I

With theforegoing general objects, features and results in view, as well as certain other 010- with boilers generally of the broad types embodying fire tubes with a recirculating chamber. for changing the direction of flow and directing the hot gasses and products of combustion from ofi and seal such a recirculating chamber from an: adjacent or surrounding chamber.

ing 'lll'sp'aced a distance inwardly from'the outer"" end thereof by an outwardly directed, peripheral flange Ila therearound which is secured to the boiler casing I0, in any suitable manner familiar in the art. The boiler is provided at the rear end of the casing ID with a transverse wall or tube sheet I2 which is secured in position disposed transversely across the casing ID spaced a distance inwardly from'the outer rear end of the casing by an outwardly directed peripheral flange I2d, similar to the flange No of the tube sheet I I at the forward end of the boiler.

A combustion tube I4 is provided disposed longitudinally of an extending generally centrally through the boiler casing I from the forward end wall II, and this combustion tube I4, in this instance, in accordance with the illustrated adaptation of my invention, terminates spaced a distance inwardly within the casing II! from the rear end wall or tube sheet I2. The combustion tube I4 is of generally cylindrical cross section and, in this instance, is of substantially uniform diameter throughout its length and may be of straight, smooth internal surface, or may be provided with annular corrugations therearound spaced longitudinally therealong, or may be formed and provided with suitable refractory or the like material, linings, as may be found expedient in any particular use, all of which constructions and arrangements of the combustion tube are familiar and Well known in the art and have no limiting effect on and are not critical to my present invention.

In this instance, the combustion tube i i extends outwardly through and is suitably secured in a centrally located circular opening in the forward tube sheet II, which opening is surrounded and defined by a forwardly extended annular flange I'Ib, is bent up and formed from the wall II and secured in any suitable manner to and around the exterior of the combustion tube I4 to form a water-tight joint with the exterior urface of the combustion tube. The combustion tube I4 at the forward end thereof extends a distance outwardly beyond the tube sheet I I of the boiler casing II] to form a section or length Ida which is received and secured at its forward end in a head or end plate I5 that is secured in position across and closing the outer end of boiler casing In which extends beyond the end wall II. This head or end plate It is formed with a circular opening or aperture I5a therein and therethrough into which the forward end of the section l'4a of the combustion tube is received. The combustion tube section I ia is received and secured in opening I5a of head plate I5 with the tube section forming a casetight sealed joint with the edge of the head I5 surrounding and defining the opening I5a therethrough. Thus, an annular chamber I 6 is formed around and surrounding the extended section I4a of the combustion tube I4, between the tube sheet II and the end plate I5, and the casing III and the combustion tube section l4a.

In this particular type of boiler construction designed for burning fluid fuel, the section I4a of the combustion tube I4 is provided with a suitable refractory or fire and heat resistant material block I! which is formed with a conical chamber therein coaxial with the tube I4 and diverging or increasing in diameter outwardly to its discharge end, which end, in the example hereof, is of a diameter substantially equal to the diameter of the combustion tube I4. A suitable fuel burner, such as an oil or gas burner nozzle I8, is mounted to discharge at the inner end of the chamber Ha within the block II. Such burner nozzle I8 is, in this instance, mounted extending axially through the block I1, and a suitable base or holder plate I8a, is mounted over and across the outer end of the section I411 of the combustion tube I4, which plate I8a receives and supports the block I I at the outer base side of the block.

The transverse end wall I2 located at the rear end of the boiler casing I0 opposite that end of the boiler in which the burner nozzle I8 is located, is formed with a central, circular opening I2a therethrough coaxial with the combustion tube I4 and of greater diameter than the diameter of the combustion tube. In this particular example of the invention, the diameter of the opening i2a in the boiler end wall I2 is approximately twice the internal diameter of the combustion tube I4, although my invention is in no sense limited or restricted to such relationship between the diameter of the aperture I2a of the end wall I2 and the internal diameter of the combustion tube I4, such relationship in this specific example being primarily dictated by the location of the inner bank of fire tubes F which have their rear ends located within the projected area of the openin I2a of wall I2 and generally intermediately located between the outer edge of such opening and the adjacent end of the combustion tube I4.

In accordance with my invention, a unitary, circular head 20 is provided for mounting in and closing the opening I2a in the end wall I2 of the boiler, to form and complete such end wall, and to provide by its design and construction the side wall around and surrounding and defining the gas recirculating chamber, separating such gas recirculating chamber from the surrounding gas chamber, as will be hereinafter fully described and explained.

The head 20 is preferably constructed as an integral, unitary structure formed of a suitable sheet or metal plate so as to provide a base or body wall 2I having an annular peripheral flange 22 thereon, bent-up or otherwise formed from the body of the head and extending from and around the periphery of the body wall 2| from one side thereof, being disposed in a plane generally perpendicular or at an angle of approximately to the plane of the body wall 2|. Thus, the head 20 is of a generally dished or cup-like form. The base or body wall 2| of the head unit 20 is provided with a central aperture 2Ia therethrough surrounded by a flange portion 23 which is bent or otherwise formed from the portion of the body wall 2I surrounding such aperture or opening 2 la and which extends outwardly from the opposite side of the body or base wall 2I from that at which the peripheral flange or annular peripheral wall 22 extends. The flange 23 at its outer edge portion has an internal diameter corresponding to the internal diameter of the rear end of the combustion tube I4, and in this instance has an external diameter substantially the same as the external diameter of the rear end of tube I4. The outer edge of this flange 23 is adapted to be secured and fixed to the rear edge of the rear end of tube I4, so that, the flange forms a longitudinal, rearward continuation of the tube and provides in effect a discharge mouth for the combustion tube I4, opening through the base wall 2I of of the head unit 20 and dischargin into the space surrounded by the annular peripheral flange 22 of the unit 20 at the rear side thereof.

The head unit 20 is mounted in the aperture I 2a of the end wall I2 of the boiler casing II], to

form and complete such end wall, by attaching ttttat ts base wall2I of the unit 20 disposed at the for ward side thereof spaced inwardly from-and generan'y parallel to the wall I2"-wi thin the boilercasing- I Il,and with the flange 22; at the opposite or rear side of the unitextended rearwardlyfa distance beyond the-end wall I2toprovide an an nular'side wall portion 24 disposed within the space defined and surrounded by the portion of the boiler casing I0 whichis-extended rearwardly beyond-the end wall I2 and its securing fiange'l 2a,.

The 'edge portion of the wallI'2' which surrounds the opening 12a. in which the unit 20 'is mounted and which is closed by such unit, is secured to and around the exterior side'o fthe flange ,22'toj form a water and gas tight joint therewith, as

welding the same to the flange 22. V I I In such mounted position of the head unit 20, the'inwardly extended flange 23 which surrounds the opening 2Ia in the body wall 2I of the unit 20, is axially alined with the combustion tube I4 and joins with and forms a longitudinal continuation rearwardly, of the wall of the tube I4. The rearend edge portion of the wall or tube I4 is i joined and fixed to the adjacent forward edge portion of the flange 23, preferably by welding, to form a water and gas tight'joint, and in effect toprovide the rear discharge end of the tube ,I4f with a rear discharge mouth opening into the space at the rear side ofthe bodywall 2! of unit tending flange 22 of the unit. Preferably, as in th'ejjspecific example hereof, the flange 23 is curved at its rear side radially outwardly and merges into the wall 2I of the unit 20, so as to provide the rear discharge end of the discharge mouth for the combustion tube I'4,' as of increasing internal diameter rearwardly, and without an abrupt or" sljiarp'shoulder therearound at the discharge end,

aiding in the smooth flow and equal dis- L tribution of the hot gasses and products] of com;

bustion from the combustion tube I 4.

The boiler of the particular example here se-l le'cted, is of. the multi-pass type, being specifically ofj thertwo-p'ass type in which the gasses and products of combustion'from the combustion tube I4 have their direction of flow reversed in an recirculating chamber of which the unit 20 forms I th'eforward and side walls, and aredirected and circulated forwardly through an'inner bank of, fii'e .tubes F surrounding/and spaced from" the 20 jwithin'and surrounded by the rearwardly exwalls! I and} Iv,,, e pect ve y, helngtfix dandhsegt cured insuchwalls to form a water'andfgastight; joint therewith, in the usual' mann'er familiar: in'this art. The firetubes F at their "rear ends extend throughand'are secured in and spaced; apart around the wall 2I of the unit 20 inter mediate the flange 22 and the discharge mouth defining flange '23 for the combustion tube {I415 as will 'be clear by reference to the drawings; The outer or secondbank of fire tubes F ,exten'df between the forward end wall I I and the rear end wall I2 of theboiler casingIO, and are secured" with their opposite ends extended'through and;

forming water and gas tight joints with such walls, respectively. In this instance, the fire tubes F are located and positioned with their rear en s"; secured in and extending through the'wall I2,}; adjacent but "spaced from the wall formed'by l. the flange 22 of the head unit 2f). v The unit 20 provides a re-entrant, indentedo'r forwardly recessed portion of the rear endwall or tube sheet I2of the boiler, with the transverse l ly disposed base or body wall 2| of the unit forwardly offset inwardly from the plane of the'wall I2, and with the combustion tube I4' attached.

and discharging'rearwardly therethrou'gh into theiga space surrounded and defined by'the peripheral side wall 22. By thus forwardlytand inwardly offsetting the body Wall 2| ofthe unit 20, and" securing and joining the end 'wall 1 I2 to and;

around the exterior of the peripheral'side wall" 22 'of unit 20 adjacent but spaced a distance in' wardly from the outer rear edge of the peripheral: side Wall forming flange 22, this peripheral side;

. wall 22 extends for the major portion of its width? into the Water space formed Within the boiler; casing I0 and is thus surrounded bya body of water in direct contact and heat exchange rela- 1 tion with the exterior surface of the wall 22, as

indicated at the locations W on the drawings. In t this manner the peripheral side wall formed by combustion tube I4. The fire tubes F discharge gasesinto the gas chamber I6, at the forward endfo'f the boiler and such gases are directed smokebox from which the gasest'iredischarg'ged "from the'boiler. W

fln the specific design and. varrangement 'of a boilerembodying my invention of the p rtic'ul'ar example here selected, the inner or first bank of ifire tubes F extendbet'ween' the forward end walljII of the boiler casing I0. and the body or,

base wall '21 of the unit 20 which forms a part otftherear end wall I2 of the boiler casing Ill;

Thejfire tubes F of the inner bank are secured ith ewe-F sewage; Peseta at the flange 22 of unit 23 is effectively water cooled; against the high temperatures to which this wall' is subjected by the hot gases and products oft combustion discharged from the combustion tube It into contact and heat exchange relation with? the inner side or interior surface of the wall 22., At the rear or smokebox end vof the boiler of,

this specific example, the rear or outer end of the" boilercasing In which extends outwardly beyond end of the boiler casing I0. At its inner side this end wall 3| is provided with a centrally locatedannular wall 32 which extends a distance in-; wardly from the inner side of wall 3|, perpenboiler. vided with a transverse wall 33 secured in position therein and thereacross intermediate the width of the wall 32, and a suitable refractory material block or disk 34 is seated and supported on the transverse base wall 33 secured in position in the head 30 and of a diameter to occupy and fill the space within and defined by the annular wall 32 and the transverse wall 33. The; inner or forward face or side 34a of the refractory material block 34 is formed concave ,for a T purpose referred V to and explained hereinafter. The refractory material block or disk 34 is formed with an annular peripheral groove therearound 1.. tiih ianstsi et er of ur oundin the..c n ve inner face 34a, and a sealing ring or gasket 35 of a suitable fire and heat resisting material, is seated and secured in such groove at the inner face or side of block 34 surrounding the concave face 34a of the block.

The end closure head 30 of the boiler is preferably removably mounted, as for example, by mounting one side of the wall 3| on suitable hinges in a manner familiar in this art, with the outer peripheral edge portion of the wall 3] being suitably removably bolted to the rear end of the wall of the boiler casing III. In the accompanying drawings the end head 30 is disclosed in its mounted position closing the end of the boiler casing and thus forming an annular chamber V within the boiler casing between the end Wall l2 and the rear or outer wall 3! of the head, and the annular wall of the casing in and the inner annular wall 32 of the head 30. This annular chamber V thus formed with the head 30 in mounted position, provides a gas vent or smokebox into which the second bank of fire tubes F discharge through the end wall [2, as will be clear by reference to Fig. 1 of the drawings. The gas chamber or smokebox V is provided with a suitable discharge outlet S by which the hot gases and products of combustion may pass and discharge from the chamber V.

The refractory material block or disk 34 at the inner side of the head 30 is coaxial with the combustion tube l4 when the head 30 is in mounted, closed position and is of a diameter such that when in closed position the sealing ring 35 is alined with the rear edge of the peripheral side wall 22 of the unit 20, and is tightly forced against and engaged with the rear edge of wall 22 to form a gas tight joint therewith to seal the chamber V from the space within and surrounded by wall 22. The head 30 in mounted closed position thus forms with the unit of the end wall l2, a gas recirculating chamber R having its rear wall formed by the refractory material block or disk 34, its forward or inner wall formed by the body wall 2| of the unit 20 and its peripheral or annular side wall formed by the flange 22 of the unit 29 together with the annular wall 32 of head 30, with the combustion tube l4 discharging into this chamber R through the wall 2|, and with the gases discharging and flowing from the chamber R into the inner or first bank of fire tubes F.

By this construction and arrangement it is to be note that the major portion of the inner side wall of the chamber or smokebox V is provided and formed by the wall 32 of the head 30, and that this inner side wall of chamber V is completed by that portion of the annular flange 22 of the head 26 which extends rearwardly beyond the end wall or crown sheet l2, with this projected portion of the flange 22 forming but a small portion of the inner Wall of the smokebox V. It is to be also noted that by this construction the flange 22 of the unit 20 forms the entire peripheral side wall for the gas recirculating chamber R, but that the major portion of this side wall 22 is surrounded by the body of water within the boiler and is thus effectively water cooled against the high temperatures to which it is subjected at its inner side by the hot gases discharged into the chamber R from the combustion tube M.

In the operation of the boiler of the present example, the hot gases and products of combustion pass rearwardly through the combustion tube M from the burner 18 at the forward end thereof and are discharged at the rear end of the tube through the discharge mouth 23 formed in the Wall 2| of the unit 20, into gas recirculating chamber R Where the gases have their direction of flow reversed and pass into and forwardly through the first or inner bank of fire tubes F into the forward gas chamber Hi. The gases in the chamber 16 have their direction of flow reversed and are directed into and flow rearwardly through the outer or second bank of fire tubes F from which they discharge into a gas chamber or smokebox V. In the recirculating chamber R the reversal of the direction of flow and the distribution of the gases into the fire tubes F, is guided and aided by the concave inner surface or face 34a of the refractory material disk 34 which is mounted coaxial with the combustion tube I4 and the discharge mouth 23 through which the gases discharge into the chamber R.

While the flange 22 of the unit 2b, which forms the peripheral side wall of the recirculating chamber R, is constantly subjected to the high temperatures of the gases discharged into the chamber R from the combustion tube It, the major area of the external surface of this flange is water cooled by the body of water in the boiler, and the joint, which is preferably formed by welding, between the edge portion of the wall l2 around the opening l2a therein, and the exterior surface of the flange 22, is also the beneficiary of this water cooling, so that, strains and stresses to which this joint may be subjected due to contraction and expansion in the operation of the boiler, are maintained at a minimum. The only portion of the flange 22 which is not directly water cooled is the portion of relatively small width which projects rearwardly beyond the wall 12, but this portion is itself immediately proximate to the water cooled portion of the flange 22, and in addition is directly in contact with the fire and heat resistant material sealing ring 35. A construction in accordance with my invention, therefore, such as the construction and arrangement of the present example, re-

duces the difficulties hereinbefore discussed, which are encountered with prior constructions in which a separate ring member is utilized to form the dividing or separating wall between a gas recirculating chamber and a surrounding gas chamber or smokebox. The unit 20 with the flange 22 and with the combustion tube discharge mouth forming flange 23, formed integral with the base wall 2|, provides a structure of extreme simplicity which can be readily manufactured, and which when assembled to form the construction and arrangement in accordance with my invention, reduces to a minimum structural failures due to contraction and expansion and other operating conditions encountered.

While in the preferred construction herein illustrated and described as an example, I have shown the head unit 20 as a separate member secured to the transverse end wall or crown sheet 12, my invention is not limited to such construction, as if desired or found expedient the wall l2 and unit 20 may be formed in one-piece or integral with a separate sealing ring forming member 24 secured or attached thereto to form a portion of the wall separating chambers R and V. In such construction the water cooling of the flange or wall 22 of the indented head is efiective to minimize the effect on the sealing ring 24 and the attaching joint between such ring and the integral Wall I2 and head 20, of

the" high temperatures under operating conditions.

Further, attention is directed to the fact that my invention contemplates and includes the formation of the integral or one piece wall l2 and indented head 2!], with the sealing ring or wall 24, also formed integral therewith, in the form of a suitable annular bead or rib for sealing engagement with the wall formed by block 34, or other structure for sealing contact with such a ring 24.

The provision of the refractory material block or disk to form the rear wall of the recirculating chamber R, with its concave inner face or surface, materially aids in the reversal of the direction of flow and the distribution of the gases in the chamber. The provision of the fire and heat resisting material sealing ring 35 which engages and forms a sealing contact with'the edged the recirculating chamber side wall forming flange 22, insures a tight joint and an efficient seal between the chambers R and V, and further provides a sealing arrangement which is resistant to and will stand up under the temperature ,and other conditions encountered in the operation of the boiler. It is also evident that various other forms, de-

j signs, arrangements and constructions ofparts and elements, as well ascombinations of parts and elements, might be resorted to without de- ,parting from the broad spirit and scope of my invention, hence I do not desire to limit my insvention in all respects" to the exact and specific disclosures hereof. I v

WhatI'claim'isiT' f 1. In boiler construction, in combinationj a boiler casing; an end wall disposed transversely of the casing'and having an inwardly indented. "central portion of a diameter less than them- "ternal diameter of said casing} said indented portion being comprised of, a wall disposed transversely of the casingand offset. inwardly. relative to said end wall, an annular flange'e'xtending, laterally outwardly from said offset wall to and being joined with said end wall; said flange being extended a distance outwardly beyond said end wall at the side thereof opposite the inwardly 'ofiset wall; the oifset wall of said indented porfqrrnwith said flange and vsai'd offset wall a gas circulating chamber therewithin;

and means opening into said gas circulating chamber through said offset wall of the indented portion for conducting gases from said gas circulating chamber.

2. In boiler construction, in combination, a boiler casing; an end wall disposed transversely of the casing and having an inwardly indented central portion of a diameter less than the diameter of said casing; said indented portion being comprised of a wall disposed transversely and offset inwardly of the casing from said end wall, and an annular flange integral with said offset Wall and being extended laterally outwardly therefrom to and being connected in fluid-tight relation with said end wall; said flange of the 10 indented portion being extended a distance on wardly beyond said end wall, the offset wall of the indented portion having a gas discharge opening therethrough; a combustion tube extending longitudinally of said casing at the inner side of said oifset wall and being connected to said gas discharge opening; a closure member for the outer side of said indented portion having a wall formed with a concave inner side in position closing the outer side of said indented portion to form with the flange and offset wall thereof a gas circulating chamber therewithin; a fire and heat resistant material sealing ring around the inner side of said closure member in position engaged with the outer edge of the outwardly extended portion of said flange to form therewith a sub- "stantially fluid-tight seal; and means opening into said chamber through the indented portion casing and offset inwardly from said end wall,

and an annular flange integral with said offset wall extended laterally and outwardly therefrom to and being connected with said end wall by a fluid-tight joint therebetween; said offset wall having a gas discharge opening therethrough;

, said annular flange of the indented portion being extended a distance outwardly beyond the side of said end wall opposite said oifset wall; a combustion .tube extending longitudinally of said casing at the inner side of and being connected to said discharge opening a closure wall closing the outer end of said casing adjacent said end wall; a head structure extending inwardly from said closure wall of an external diameter less than the internal diameter of said casing to form an annular chamber therearound within the casing between said end wall and the outer end closure wall of said casing; said inwardly extended head 1 structure including an inner wall of a diameter 'to close the outer' side of the space within said flange to form therewithin a gas circulating chamber; the inner side of said head structure inner wall being engaged and forming a substantially fluid-tight joint with the outer edge of the outwardly projected portion of said annular flange; and means for conducting gases from said gas circulating chamber to said annular chamber;

24'. In' boiler construction, in combination, a boiler casing; anend wall disposed transversely of s'aid -casing-and-having an opening therethrough; a closing head mounted within and closing said opening through said end wall and being comprised of a body wall disposed transversely of said casing spaced inwardly of the easing a distance from said end wall, and an annular flange therearound extending outwardly from the side of said body wall adjacent said end wall; said flange having an external diameter substantially the same as the internal diameter of said end wall opening and being extended outwardly through said opening; said end wall being connected to and around the exterior of said flange in fluid-tight relation therewith; the body wall of said head unit being formed with a gas discharge opening therethrough and an inwardly extended flange surrounding and forming a continuation of said opening; a combustion tube disposed longitudinally of said casing at the inner side of said body Wall and being connected at one end to said inwardly extended flange of said body wall, an outer head at the end of said casing adjacent said end Wall, said outer head including a refractory material wall engaged in sealing relation with the outer edge of said outwardly extended portion of the flange of said head unit closing the outer side of said head to form therewithin a gas circulating chamber; and means for conducting combustion gases from said gas circulating chamber.

5. In boiler construction, in combination, a boiler casing; an end wall disposed transversely of the casing spaced a distance inwardly from the adjacent casing end; said end wall having an inwardly indented central portion of a diameter less than the internal diameter of said casing and being comprised of a wall disposed transversely of the casing ofiset inwardly from said end wall, and an annular flange extended laterally and outwardly from said ofiset wall to and being joined with said end wall; said offset wall having a gas discharge opening therethrough; said annular flange of said indented portion being extended a distance outwardly beyond that side of said end Wall opposite the ofiset wall of said indented portion; a combustion tube in said casing at the inner side of said offset wall and being connected to said discharge opening; a head structure closing the outer side of the space within said indented portion and being engaged and forming a gastight joint with the outer edge of the outwardly projected portion of said annular flange to form therewithin a gas circulating chamber; said head structure having an external diameter less than the internal diameter of said casing; a closure wall extending across the outer end of said casing adjacent said end wall to form an annular chamber within the casing around said head structure between said end wall and said closure wall; and means for conducting gases from said gas circulating chamber to said annular chamher.

6. In boiler construction, in combination, a boiler casing; an end wall disposed transversely of said casing and including an inwardly indented portion of less diameter than the internal diameter of said casing; said indented portion comprising an ofiset Wall disposed transversely of the casing spaced a distance inwardly thereof from said end wall, and an annular flange integral with said offset wall and being extended laterally outwardly therefrom joining said end wall; the annular flange of said indented portion being extended a distance outwardly beyond the outer side of said end wall; said offset Wall having a gas discharge opening therethrough; a combustion tube in said casing at the inner side of said oifset wall and being connected to said as discharge pening; a fire and heat resistant material wall across the outer edge portion of said annular flange in sealing engagement therewith to seal off the space between said ofiset wall 5 and flange to form therewithin a gas recirculating chamber; the inner side of said fire and heat resistant material wall being formed with a concave portion substantially coaxial with the opening through the offset wall of said indented porl l tion; and means opening through the offset wall of said indented portion between the annular flange thereof and said combustion tube for conducting gases from said recirculating chamber. '7. In boiler construction, in combination, a 15 boiler casing; an end wall disposed transversely of said casing spaced inwardly a distance from the adjacent casing end and including an inwardly indented portion having a diameter less than the internal diameter of said casing; said 530 indented portion comprising, a wall disposed transversely of the casing offset inwardly from said end wall, and an annular flange extended laterally outwardly from said oflset Wall and being joined with said end wall; said annular flange 25 being extended outwardly a distance beyond the outer side of said end wall; said ofiset wall having a gas discharge opening therethrough; a combustion tube in said casing at the inner side of said ofiset wall and being connected to said :20 gas discharge opening; a closure head secured in position closing the outer end of the outwardly projected portion of said annular flange in sealing engagement with the outer edge portion thereof, said closure head, annular flange and in- 3 wardly ofiset wall together forming a gas recirculating chamber therewithin; and a closure wall structure in the end of said boiler casing adjacent said end wall forming a gas chamber within the casing surrounding the outwardly projected portion of said annular flange and said closure head thereon; and means in said casing at the inner side of said end wall opening into said gas recirculating chamber through said offset wall for conducting gases from said chamber to said surrounding chamber.

HENRY W. LYKE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

